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• Some general C questions.

  - by b-gen-jack-o-neill

  Hello. I am trying to fully understand the process pro writing code in some language to execution by OS. In my case, the language would be C and the OS would be Windows. So far, I read many different articles, but I am not sure, whether I understand the process right, and I would like to ask you if you know some good articles on some subjects I couldn´t find. So, what I think I know about C (and basically other languages): C compiler itself handles only data types, basic math operations, pointers operations, and work with functions. By work with functions I mean how to pass argument to it, and how to get output from function. During compilation, function call is replaced by passing arguments to stack, and than if function is not inline, its call is replaced by some symbol for linker. Linker than find the function definition, and replace the symbol to jump adress to that function (and of course than jump back to program). If the above is generally true and I get it right, where to final .exe file actually linker saves the functions? After the main() function? And what creates the .exe header? Compiler or Linker? Now, additional capabilities of C, today known as C standart library is set of functions and the declarations of them, that other programmers wrote to extend and simplify use of C language. But these functions like printf() were (or could be?) written in different language, or assembler. And there comes my next question, can be, for example printf() function be written in pure C without use of assembler? I know this is quite big question, but I just mostly want to know, wheather I am right or not. And trust me, I read a lots of articles on the web, and I would not ask you, If I could find these infromation together on one place, in one article. Insted I must piece by piece gather informations, so I am not sure if I am right. Thanks.

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• Adapting existing HTML/Javascript model to Titanium's latest release (v 0.9)

  - by Alan Neal

  In pre-0.9 versions of Titanium, one could simply specify an .html file (local or remote) in the tiapp.xml file and interact with it in the same manner as one would on a website. As of version 0.9, that is no the longer case. One creates their entire app dynamically. Unfortunately, this broke my previous implementation and, other than an updated Kitchen Sink, much of the new model and API calls are not covered in the documentation (e.g., createLabel). So, my question is this... What are the simplest steps for re-creating the previous effect (knowingly forgoing some of the advantages of the Titanium's latest approach if necessary)? My previous implementation was exactly as it functions on the website. The website has a single index.html file with no content other than links to JavaScript and style files. The document body's onload event called the first JavaScript function (located in the main script) and, from that point forth, the entire content was dynamically created. How can I set up the latest version of Titanium so that I am poised to do the exact same thing? BTW: Whereas I previously had the choice to keep the files local or remote, I don't believe that remote access (e.g., simply using the webView widget to point to the website) is viable. That's because pages displayed via the webView do not have access to most of the API. Since the iPhone and Safari browsers do not support the file input type, the only means for uploading files (something my app requires) is calling Titanium's function. Thanks in advance.

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• Problem Activating Sharepoint Timer Job

  - by Ben Robinson

  I have created a very simple sharepoint timer job. All i want it to do is iterate through a list and update each list item so that it triggers an existing workflow that works fine. In other words all i am trying to do is work around the limitation that workflows cannot be triggered on a scheduled basis. I have written a class that inherits from SPJobDefinition that does the work and i have a class that inherits from SPFeatureReceiver to install and activate it. I have created the feature using SPVisualdev that my coleagues have used in the past for other SP development. My Job class is below: public class DriverSafetyCheckTrigger : SPJobDefinition { private string pi_SiteUrl; public DriverSafetyCheckTrigger(string SiteURL, SPWebApplication WebApp):base("DriverSafetyCheckTrigger",WebApp,null, SPJobLockType.Job) { this.Title = "DriverSafetyCheckTrigger"; pi_SiteUrl = SiteURL; } public override void Execute(Guid targetInstanceId) { using (SPSite siteCollection = new SPSite(pi_SiteUrl)) { using (SPWeb site = siteCollection.RootWeb) { SPList taskList = site.Lists["Driver Safety Check"]; foreach(SPListItem item in taskList.Items) { item.Update(); } } } } } And the only thing in the feature reciever class is that i have overridden the FeatureActivated method below: public override void FeatureActivated(SPFeatureReceiverProperties Properties) { SPSite site = Properties.Feature.Parent as SPSite; // Make sure the job isn't already registered. foreach (SPJobDefinition job in site.WebApplication.JobDefinitions) { if (job.Name == "DriverSafetyCheckTrigger") job.Delete(); } // Install the job. DriverSafetyCheckTrigger oDriverSafetyCheckTrigger = new DriverSafetyCheckTrigger(site.Url, site.WebApplication); SPDailySchedule oSchedule = new SPDailySchedule(); oSchedule.BeginHour = 1; oDriverSafetyCheckTrigger.Schedule = oSchedule; oDriverSafetyCheckTrigger.Update(); } The problem i have is that when i try to activate the feature it throws a NullReferenceException on the line oDriverSafetyCheckTrigger.Update(). I am not sure what is null in this case, the example i have followed for this is this tutorial. I am not sure what I am doing wrong.

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• Access denied error on select into outfile using Zend

  - by Peter

  Hi, I'm trying to make a dump of a MySQL table on the server and I'm trying to do this in Zend. I have a model/mapper/dbtable structure for all my connections to my tables and I'm adding the following code to the mappers: public function dumpTable() { $db = $this->getDbTable()->getAdapter(); $name = $this->getDbTable()->info('name'); $backupFile = APPLICATION_PATH . '/backup/' . date('U') . '_' . $name . '.sql'; $query = "SELECT * INTO OUTFILE '$backupFile' FROM $name"; $db->query( $query ); } This should work peachy, I thought, but Message: Mysqli prepare error: Access denied for user 'someUser'@'localhost' (using password: YES) is what this results in. I checked the user rights for someUser and he has all the rights to the database and table in question. I've been looking around here and on the net in general and usually turning on "all" the rights for the user seems to be the solution, but not in my case (unless I'm overlooking something right now with my tired eyes + I don't want to turn on "all" on my production server). What am I doing wrong here? Or, does anybody know a more elegant way to get this done in Zend?

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• Winforms: How to speed up Invalidate()?

  - by Pedery

  I'm developing a retained mode drawing application in GDI+. The application can draw simple shapes to a canvas and perform basic editing. The math that does this is optimized to the last byte and is not an issue. I'm drawing on a panel that is using the built-in Controlstyles.DoubleBuffer. Now, my problem arises if I run my app maximized on a big monitor (HD in my case). If I try to draw a line from one corner of the (big) canvas to the diagonally oposite other, it will start to lag and the CPU goes high up. Each graphical object in my app has a boundingbox. Thus, when I invalidate the boundingbox of a line that goes from one corner of the maximized app to the oposite diagonal one, that boundingbox is virtually as big as the canvas. When a user is drawing a line, this invalidation of the boundingbox thus happens on the mousemove event, and there is a clear lag visible. This lag also exists if the line is the only object on the canvas. I've tried to optimize this in many ways. If I draw a shorter line, the CPU and the lag goes down. If I remove the Invalidate() and keep all other code, the app is quick. If I use a Region (that only spans the figure) to invalidate instead of the boundingbox, it is just as slow. If I split the boundingbox into a range of smaller boxes that lie back to back, thus reducing the invalidation area, no visible performance gain can be seen. Thus I'm at a loss here. How can I speed up the invalidation? On a side note, both Paint.Net and Mspaint suffers from the same shortcommings. Word and PowerPoint however, seem to be able to paint a line as described above with no lag and no CPU load at all. Thus it's possible to achieve the desired results, the question is how?

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• 'memcache-client' problem - app can't load the gem

  - by Max Williams

  Hi all - i'm trying to get memcached and the Interlock plugin working with a new rails app. The weird thing is that they both work fine in another app on the same machine and i can't figure out the difference that's stopping this app. The new app is rails 2.3.4 and the old one is 2.2.2 in case that's a factor. When the app starts, i get a warning from interlock: `install_memcached':Interlock::ConfigurationError: 'memcache-client' client requested but not installed. Try 'sudo gem install memcache-client'. Now, i have memcache-client installed: $> gem list | grep memcache memcache-client (1.7.8) The gem is in /var/lib/gems/1.8, which is in my GEM_PATH variable. On a bit of further investigation, the above error is raised by interlock when it refers to the MemCache class, which doesn't exist and so raises an 'anonymous module' error. So, ultimately, the problem is that MemCache isn't loaded. I have a memcached.yml in my config folder (below) however. I'm stuck - any advice anyone? #contents of config/memcached.yml defaults: namespace: millionaire #sessions: true sessions: false client: memcache-client with_finders: true development: servers: - 127.0.0.1:11211 production: servers: - 127.0.0.1:11211

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• Webservice returning 403 error

  - by user48408

  I'm wondering whether I'm receiving the 403 errors because there are too many attempted connections being made to the webservice. If this is the case how do I get around it? I've tried creating a new instance of InternalWebService each time and disposing of the old one but I get the same problem. I've disabled the firewall and the webservice is located locally at the moment. I beginning to think it may be a problem with the credentials but the control tree is populated via the webservice at some stage. If I browse to the webmethods in my browser I can run them all. I return an instance of the webservice from my login handler loginsession.cs: static LoginSession() { ... g_NavigatorWebService = new InternalWebService(); g_NavigatorWebService.Credentials = System.Net.CredentialCache.DefaultCredentials; ... } public static InternalWebService NavigatorWebService { get { return g_NavigatorWebService; } } I have a tree view control which uses the webservice to populate itself. IncidentTreeViewControl.cs: public IncidentTreeView() { InitializeComponent(); m_WebService = LoginSession.NavigatorWebService; ... } public void Populate() { m_WebService.BeginGetIncidentSummaryByCompany(new AsyncCallback(IncidentSummaryByClientComplete), null); m_WebService.BeginGetIncidentSummaryByDepartment(new AsyncCallback(IncidentSummaryByDepartmentComplete), null); ... } private void IncidentSummaryByClientComplete(IAsyncResult ar) { MyTypedDataSet data = m_WebService.EndGetIncidentSummaryByCompany(ar); //403 ..cont... } I'm getting the 403 on the last line.

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• What are alternatives to Win32 PulseEvent() function?

  - by Bill

  The documentation for the Win32 API PulseEvent() function (kernel32.dll) states that this function is “… unreliable and should not be used by new applications. Instead, use condition variables”. However, condition variables cannot be used across process boundaries like (named) events can. I have a scenario that is cross-process, cross-runtime (native and managed code) in which a single producer occasionally has something interesting to make known to zero or more consumers. Right now, a well-known named event is used (and set to signaled state) by the producer using this PulseEvent function when it needs to make something known. Zero or more consumers wait on that event (WaitForSingleObject()) and perform an action in response. There is no need for two-way communication in my scenario, and the producer does not need to know if the event has any listeners, nor does it need to know if the event was successfully acted upon. On the other hand, I do not want any consumers to ever miss any events. In other words, the system needs to be perfectly reliable – but the producer does not need to know if that is the case or not. The scenario can be thought of as a “clock ticker” – i.e., the producer provides a semi-regular signal for zero or more consumers to count. And all consumers must have the correct count over any given period of time. No polling by consumers is allowed (performance reasons). The ticker is just a few milliseconds (20 or so, but not perfectly regular). Raymen Chen (The Old New Thing) has a blog post pointing out the “fundamentally flawed” nature of the PulseEvent() function, but I do not see an alternative for my scenario from Chen or the posted comments. Can anyone please suggest one? Please keep in mind that the IPC signal must cross process boundries on the machine, not simply threads. And the solution needs to have high performance in that consumers must be able to act within 10ms of each event.

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• Problem counting item frequency on T-SQL

  - by Raúl Roa

  I'm trying to count the frequency of numbers from 1 to 100 on different fields of a table. Let's say I have the table "Results" with the following data: LottoId Winner Second Third --------- --------- --------- --------- 1 1 2 3 2 1 2 3 I'd like to be able to get the frequency per numbers. For that I'm using the following code: --Creating numbers temp table CREATE TABLE #Numbers( Number int) --Inserting the numbers into the temp table declare @counter int set @counter = 0 while @counter < 100 begin set @counter = @counter + 1 INSERT INTO #Numbers(Number) VALUES(@counter) end -- SELECT #Numbers.Number, Count(Results.Winner) as Winner,Count(Results.Second) as Second, Count(Results.Third) as Third FROM #Numbers LEFT JOIN Results ON #Numbers.Number = Results.Winner OR #Numbers.Number = Results.Second OR #Numbers.Number = Results.Third GROUP BY #Numbers.Number The problem is that the counts are repeating the same values for each number. In this particular case I'm getting the following result: Number Winner Second Third --------- --------- --------- --------- 1 2 2 2 2 2 2 2 3 2 2 2 ... When I should get this: Number Winner Second Third --------- --------- --------- --------- 1 2 0 0 2 0 2 0 3 0 0 2 ... What am I missing?

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• Setting nested object to null when combobox has empty value

  - by Javi

  Hello, I have a Class which models a User and another which models his country. Something like this: public class User{ private Country country; //other attributes and getter/setters } public class Country{ private Integer id; private String name; //other attributes and getter/setters } I have a Spring form where I have a combobox so the user can select his country or can select the undefined option to indicate he doen't want to provide this information. So I have something like this: <form:select path="country"> <form:option value="">-Select one-</form:option> <form:options items="${countries}" itemLabel="name" itemValue="id"/> </form:select> In my controller I get the autopopulated object with the user information and I want to have country set to null when the "-Select one-" option has been selected. So I have set a initBinder with a custom editor like this: @InitBinder protected void initBinder(WebDataBinder binder) throws ServletException { binder.registerCustomEditor(Country.class, "country", new CustomCountryEditor()); } and my editor do something like this: public class CustomCountryEditor(){ @Override public String getAsText() { //I return the Id of the country } @Override public void setAsText(String str) { //I search in the database for a country with id = new Integer(str) //and set country to that value //or I set country to null in case str == null } } When I submit the form it works because when I have country set to null when I have selected "-Select one-" option or the instance of the country selected. The problem is that when I load the form I have a method like the following one to load the user information. @ModelAttribute("user") public User getUser(){ //loads user from database } The object I get from getUser() has country set to a specific country (not a null value), but in the combobox is not selected any option. I've debugged the application and the CustomCountryEditor works good when setting and getting the text, thoughgetAsText method is called for every item in the list "countries" not only for the "country" field. Any idea? Is there a better way to set null the country object when I select no country option in the combobox? Thanks

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• Designing a fluid Javascript interface to hide callback asynchrony

  - by Anurag

  How would I design an API to hide the asynchronous nature of AJAX and HTTP requests, or basically delay it to provide a fluid interface. To show an example from Twitter's new Anywhere API: // get @ded's first 20 statuses, filter only the tweets that // mention photography, and render each into an HTML element T.User.find('ded').timeline().first(20).filter(filterer).each(function(status) { $('div#tweets').append('<p>' + status.text + '</p>'); }); function filterer(status) { return status.text.match(/photography/); } vs this (asynchronous nature of each call is clearly visible) T.User.find('ded', function(user) { user.timeline(function(statuses) { statuses.first(20).filter(filterer).each(function(status) { $('div#tweets').append('<p>' + status.text + '</p>'); }); }); }); It finds the user, gets their tweet timeline, filters only the first 20 tweets, applies a custom filter, and ultimately uses the callback function to process each tweet. I am guessing that a well designed API like this should work like a query builder (think ORMs) where each function call builds the query (HTTP URL in this case), until it hits a looping function such as each/map/etc., the HTTP call is made and the passed in function becomes the callback. An easy development route would be to make each AJAX call synchronous, but that's probably not the best solution. I am interested in figuring out a way to make it asynchronous, and still hide the asynchronous nature of AJAX.

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• Using Directives, Namespace and Assembly Reference - all jumbled up with StyleCop!

  - by Jack

  I like to adhere to StyleCop's formatting rules to make code nice and clear, but I've recently had a problem with one of its warnings: All using directives must be placed inside of the namespace. My problem is that I have using directives, an assembly reference (for mocking file deletion), and a namespace to juggle in one of my test classes: using System; using System.IO; using Microsoft.Moles.Framework; using Microsoft.VisualStudio.TestTools.UnitTesting; [assembly: MoledType(typeof(System.IO.File))] namespace MyNamespace { //Some Code } The above allows tests to be run fine - but StyleCop complains about the using directives not being inside the namespace. Putting the usings inside the namespace gives the error that "MoledType" is not recognised. Putting both the usings and the assembly reference inside the namespace gives the error 'assembly' is not a valid attribute location for this declaration. Valid attribute locations for this declaration are 'type'. All attributes in this block will be ignored. It seems I've tried every layout I can but to no avail - either the solution won't build, the mocking won't work or StyleCop complains! Does anyone know a way to set these out so that everything's happy? Or am I going to have to ignore the StyleCop warning in this case?

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• Why can't the compiler/JVM just make autoboxing "just work"?

  - by Pyrolistical

  Autoboxing is rather scary. While I fully understand the difference between == and .equals I can't but help have the follow bug the hell out of me: final List<Integer> foo = Arrays.asList(1, 1000); final List<Integer> bar = Arrays.asList(1, 1000); System.out.println(foo.get(0) == bar.get(0)); System.out.println(foo.get(1) == bar.get(1)); That prints true false Why did they do it this way? It something to do with cached Integers, but if that is the case why don't they just cache all Integers used by the program? Or why doesn't the JVM always auto unbox to primitive? Printing false false or true true would have been way better. EDIT I disagree about breakage of old code. By having foo.get(0) == bar.get(0) return true you already broke the code. Can't this be solved at the compiler level by replacing Integer with int in byte code (as long as it is never assigned null)

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• Unit testing JSON output module, best practices

  - by Banang

  I am currently working on a module that takes one of our business objects and returns a json representation of that object to the caller. Due to limitations in our environment I am unable to use any existing json writer, so I have written my own, which is then used by the business object writer to serialize my objects. The json writer is tested in a way similar to this @Test public void writeEmptyArrayTest() { String expected = "[ ]"; writer.array().endArray(); assertEquals(expected, writer.toString()); } which is only manageable because of the small output each instruction produces, even though I keep feeling there must be a better way. The problem I am now facing is writing tests for the object writer module, where the output is much larger and much less manageable. The risk of spelling mistakes in the expected strings mucking up my tests seem too great, and writing code in this fashion seems both silly and unmanageable in a long term perspective. I keep feeling like I want to write tests to ensure that my tests are behaving correctly, and this feeling worries me. Therefore, is there a better way of doing this? Surely there must be? Does anyone know of any good literature in regard to this specific case (doesn't have to be json, but you know what I mean)? Grateful for all help.

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• Deriving an HTMLElement Object from jQuery Object

  - by Jasconius

  I'm doing a fairly exhaustive series of DOM manipulations where a few elements (specifically form elements) have some events. I am dynamically creating (actually cloning from a source element) several boxes and assigning a change() event to them. The change event executes, and within the context of the event, "this" is the HTML Element Object. What I need to do at this point however is determine a contact for this HTML Element Object. I have these objects stored already as jQuery entities in assorted arrays, but obviously [HTMLElement Object] != [Object Object] And the trick is that I cannot cast $(this) and make a valid comparison since that would create a new object and the pointer would be different. So... I've been banging my head against this for a while. In the past I've been able to circumvent this problem by doing an innerHTML comparison, but in this case the objects I am comparing are 100% identical, just there's lots of them. Therefore I need a solid comparison. This would be easy if I could somehow derive the HTMLElement object from my originating jQuery object. Thoughts, other ideas? Help. :(

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• Minimal-change algorithm which maximises 'swapping'

  - by Kim Bastin

  This is a question on combinatorics from a non-mathematician, so please try to bear with me! Given an array of n distinct characters, I want to generate subsets of k characters in a minimal-change order, i.e. an order in which generation n+1 contains exactly one character that was not in generation n. That's not too hard in itself. However, I also want to maximise the number of cases in which the character that is swapped out in generation n+1 is the same character that was swapped in in generation n. To illustrate, for n=7, k=3: abc abd abe* abf* abg* afg aeg* adg* acg* acd ace* acf* aef adf* ade bde bdf bef bcf* bce bcd* bcg* bdg beg* bfg* cfg ceg* cdg* cde cdf* cef def deg dfg efg The asterisked strings indicate the case I want to maximise; e.g. the e that is new in generation 3, abe, replaces a d that was new in generation 2, abd. It doesn't seem possible to have this happen in every generation, but I want it to happen as often as possible. Typical array sizes that I use are 20-30 and subset sizes around 5-8. I'm using an odd language, Icon (or actually its derivative Unicon), so I don't expect anyone to post code that I can used directly. But I will be grateful for answers or hints in pseudo-code, and will do my best to translate C etc. Also, I have noticed that problems of this kind are often discussed in terms of arrays of integers, and I can certainly apply solutions posted in such terms to my own problem. Thanks Kim Bastin

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• BackgroundWorker From ASP.Net Application

  - by Kevin

  We have an ASP.Net application that provides administrators to work with and perform operations on large sets of records. For example, we have a "Polish Data" task that an administrator can perform to clean up data for a record (e.g. reformat phone numbers, social security numbers, etc.) When performed on a small number of records, the task completes relatively quickly. However, when a user performs the task on a larger set of records, the task may take several minutes or longer to complete. So, we want to implement these kinds of tasks using some kind of asynchronous pattern. For example, we want to be able to launch the task, and then use AJAX polling to provide a progress bar and status information. I have been looking into using the BackgroundWorker class, but I have read some things online that make me pause. I would love to get some additional advice on this. For example, I understand that the BackgroundWorker will actually use the thread pool from the current application. In my case, the application is an ASP.Net web site. I have read that this can be a problem because when the application recycles, the background workers will be terminated. Some of the jobs I mentioned above may take 3 minutes, but others may take a few hours. Also, we may have several hundred administrators all performing similar operations during the day. Will the ASP.Net application thread pool be able to handle all of these background jobs efficiently while still performing it's normal request processing? So, I am trying to determine if using the BackgroundWorker class and approach is right for our needs. Should I be looking at an alternative approach? Thanks and sorry for such a long post! Kevin

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• create app that has plugin which contains PyQt widget

  - by brian

  I'm writing an application that will use plugins. In the plugin I want to include a widget that allows the options for that plugin to be setup. The plugin will also include methods to operate on the data. What is is the best way to include a widget in a plugin? Below is pseudo code for what I've tried to do. My original plan was to make the options widget: class myOptionsWidget(QWidget): “”” create widget for plug in options “”” …. Next I planned on including the widget in my plugin: class myPlugin def __init__(self): self.optionWidget = myOptionsWidget() self.pluginNum = 1 …. def getOptionWidget(self): return(self.optionWidget) Then at the top level I'd do something like a = myPlugin() form = createForm(option=a.getOptionWidget()) … where createForm would create the form and include my plugin options widget. But when I try "a = myPlugin()" I get the error "QWidget: Must construct a QApplication before a QpaintDevice" so this method won't work. I know I would store the widget as a string and call eval on it but I'd rather not do that in case later on I want to convert the program to C++. What is the best way to write a plugin that includes a widget that has the options? Brian

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• SEO Friendly URL Rewriter Parameters

  - by Kristen

  I would appreciate you advice on how to incorporate parameters into SEO Friendly URLs We have decided to have the "techie" parameters first, followed by the "SEO Slug" \product\ABC123\fly-your-own-helicopter much like S.O. - if the SEO Slug changes, or is truncated, or missing, we still have the Product and ABC123 parameters; various articles say that having such extra data doesn't harm SEO ranking. We need to have additional parameters; we could use "-" to separate parameters as it makes them look similar to the SEO Slug, or we could/should use something else? \product\ABC123-BOYTOY-2\boys\toys\fly-your-own-helicopter This is product=ABC123, in Category=BOYTOY and Page=2. We also want to keep the hierarchy as flat as possible, and thus I think: \product-ABC123-BOYTOY-2\boys\toys\fly-your-own-helicopter would be better - one level less. We have a number of "zones", e.g. \product-ABC123\seo-slug-for-product \category-BOYTOY\seo-slug-for-category \article-54321\terms-and-conditions it would help us a lot if we could just user our 5 digit Page ID number instead, so these would become \12345-ABC123\seo-slug-for-product \23456-BOYTOY\seo-slug-for-category \54321\terms-and-conditions (Products & Categories have a number of different Page IDs for different templates, this style would take us straight to the right one) I would appreciate your insight into what parameter separators to use, and if the leading techi-data is going work well for us. In case relevant: Classic ASP application on IIS7 + MSSQL2008 Product & Category codes contain A-Z, 0-9, "_" only.

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• Does GC guarantee that cleared References are enqueued to ReferenceQueue in topological order?

  - by Dimitris Andreou

  Say there are two objects, A and B, and there is a pointer A.x --> B, and we create, say, WeakReferences to both A and B, with an associated ReferenceQueue. Assume that both A and B become unreachable. Intuitively B cannot be considered unreachable before A is. In such a case, do we somehow get a guarantee that the respective references will be enqueued in the intuitive (topological when there are no cycles) order in the ReferenceQueue? I.e. ref(A) before ref(B). I don't know - what if the GC marked a bunch of objects as unreachable, and then enqueued them in no particular order? I was reviewing Finalizer.java of guava, seeing this snippet: private void cleanUp(Reference<?> reference) throws ShutDown { ... if (reference == frqReference) { /* * The client no longer has a reference to the * FinalizableReferenceQueue. We can stop. */ throw new ShutDown(); } frqReference is a PhantomReference to the used ReferenceQueue, so if this is GC'ed, no Finalizable{Weak, Soft, Phantom}References can be alive, since they reference the queue. So they have to be GC'ed before the queue itself can be GC'ed - but still, do we get the guarantee that these references will be enqueued to the ReferenceQueue at the order they get "garbage collected" (as if they get GC'ed one by one)? The code implies that there is some kind of guarantee, otherwise unprocessed references could theoretically remain in the queue. Thanks

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• How can I improve my real-time behavior in multi-threaded app using pthreads and condition variables

  - by WilliamKF

  I have a multi-threaded application that is using pthreads. I have a mutex() lock and condition variables(). There are two threads, one thread is producing data for the second thread, a worker, which is trying to process the produced data in a real time fashion such that one chuck is processed as close to the elapsing of a fixed time period as possible. This works pretty well, however, occasionally when the producer thread releases the condition upon which the worker is waiting, a delay of up to almost a whole second is seen before the worker thread gets control and executes again. I know this because right before the producer releases the condition upon which the worker is waiting, it does a chuck of processing for the worker if it is time to process another chuck, then immediately upon receiving the condition in the worker thread, it also does a chuck of processing if it is time to process another chuck. In this later case, I am seeing that I am late processing the chuck many times. I'd like to eliminate this lost efficiency and do what I can to keep the chucks ticking away as close to possible to the desired frequency. Is there anything I can do to reduce the delay between the release condition from the producer and the detection that that condition is released such that the worker resumes processing? For example, would it help for the producer to call something to force itself to be context switched out? Bottom line is the worker has to wait each time it asks the producer to create work for itself so that the producer can muck with the worker's data structures before telling the worker it is ready to run in parallel again. This period of exclusive access by the producer is meant to be short, but during this period, I am also checking for real-time work to be done by the producer on behalf of the worker while the producer has exclusive access. Somehow my hand off back to running in parallel again results in significant delay occasionally that I would like to avoid. Please suggest how this might be best accomplished.

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• Writing String to Stream and reading it back does not work

  - by Binary255

  I want to write a String to a Stream (a MemoryStream in this case) and read the bytes one by one. stringAsStream = new MemoryStream(); UnicodeEncoding uniEncoding = new UnicodeEncoding(); String message = "Message"; stringAsStream.Write(uniEncoding.GetBytes(message), 0, message.Length); Console.WriteLine("This:\t\t" + (char)uniEncoding.GetBytes(message)[0]); Console.WriteLine("Differs from:\t" + (char)stringAsStream.ReadByte()); The (undesired) result I get is: This: M Differs from: ? It looks like it's not being read correctly, as the first char of "Message" is 'M', which works when getting the bytes from the UnicodeEncoding instance but not when reading them back from the stream. What am I doing wrong? The bigger picture: I have an algorithm which will work on the bytes of a Stream, I'd like to be as general as possible and work with any Stream. I'd like to convert an ASCII-String into a MemoryStream, or maybe use another method to be able to work on the String as a Stream. The algorithm in question will work on the bytes of the Stream.

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• Matplotlib canvas drawing

  - by Morgoth

  Let's say I define a few functions to do certain matplotlib actions, such as def dostuff(ax): ax.scatter([0.],[0.]) Now if I launch ipython, I can load these functions and start a new figure: In [1]: import matplotlib.pyplot as mpl In [2]: fig = mpl.figure() In [3]: ax = fig.add_subplot(1,1,1) In [4]: run functions # run the file with the above defined function If I now call dostuff, then the figure does not refresh: In [6]: dostuff(ax) I have to then explicitly run: In [7]: fig.canvas.draw() To get the canvas to draw. Now I can modify dostuff to be def dostuff(ax): ax.scatter([0.],[0.]) ax.get_figure().canvas.draw() This re-draws the canvas automatically. But now, say that I have the following code: def dostuff1(ax): ax.scatter([0.],[0.]) ax.get_figure().canvas.draw() def dostuff2(ax): ax.scatter([1.],[1.]) ax.get_figure().canvas.draw() def doboth(ax): dostuff1(ax) dostuff2(ax) ax.get_figure().canvas.draw() I can call each of these functions, and the canvas will be redrawn, but in the case of doboth(), it will get redrawn multiple times. My question is: how could I code this, such that the canvas.draw() only gets called once? In the above example it won't change much, but in more complex cases with tens of functions that can be called individually or grouped, the repeated drawing is much more obvious, and it would be nice to be able to avoid it. I thought of using decorators, but it doesn't look as though it would be simple. Any ideas?

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• Grails bean-fields plugin

  - by Don

  Hi, I'm having problems using the Grails bean-fields plugin with a class this is annotated Validateable, but is not a domain/command class. The root cause of the problem appears to be in this method of BeanTagLib.groovy private def getBeanConstraints(bean) { if (bean?.metaClass?.hasProperty(bean, 'constraints')) { def cons = bean.constraints if (cons != null) { if (log.debugEnabled) { log.debug "Bean is of type ${bean.class} - the constraints property was a [${cons.class}]" } // Safety check for the case where bean is no a proper domain/command object // This avoids confusing errors where constraints comes back as a Closure if (!(cons instanceof Map)) { if (log.warnEnabled) { log.warn "Bean of type ${bean.class} is not a domain class, command object or other validateable object - the constraints property was a [${cons.class}]" } } } else { if (log.warnEnabled) { log.warn "Bean of type ${bean.class} has no constraints" } } return cons } else return null } I tested out this method above in the grails console and when I pass an instance of MyBean into this method, it logs: Bean of type ${bean.class} is not a domain class, command object or other validateable object - the constraints property was a [${cons.class}] Because the constraints are returned as an instance of Closure instead of a Map. If I could figue out how to get a Map reference to the constraints of a @Validateable class (that is not a domain/command class), I guess I could resolve the problem. Thanks, Don

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• Multiselect Form Field in PDF

  - by Jason R. Coombs

  Using PDF, is it possible to create a single form element with multiple fields of which several can be selected? For example, in HTML, one can create a set of checkboxes associated with the same field name: <div>Select one for Member of the School Board</div> <input type="checkbox" name="field(school)" value="vote1"> <span class="label">Libby T. Garvey</span><br/> <input type="checkbox" name="field(school)" value="vote2"> <span class="label">Emma N. Violand-Sanchez</span><br/> In this case, the field name is "field(school)", and when the form is submitted, "field(school)" can be supplied 0, 1, or 2 times. Is there an equivalent construct in PDF where a single field can have multiple values. So far in my investigation, it appears that if fields are assigned the same name, it is only possible to select one field. If it is possible to implement this in PDF, what is this construct called and how can it be implemented? Edit: To clarify, I am aware that a PDF can contain multiple form fields with different field names, and those can be selected independently, but then the grouping is implicit and not explicit as with the HTML form. I would like to use a construct that makes the grouping of options explicit, and preferably allows for restrictions (e.g. at least one required, no more than 2 allowed, etc).

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